Severe idiopathic inflammatory myopathies (polymyositis, dermatomyositis, and related diseases) that respond poorly to corticosteroids are difficult to treat. We have undertaken three therapeutic trials for the treatment of such patients: a) a controlled double-blind trial of plasmapheresis and leukapheresis; b) an open trial of monthly intravenous cyclophosphamide; c) a controlled, crossover trial of intravenous methotrexate with leucovorin rescue and a combination of methotrexate and azathioprine. The trial of apheresis continues; 30 patients have entered so far, with a goal of 40. The trial of cyclophosphamide was terminated after 11 patients had entered because of inefficacy. The trial of i.v. methotrexate and combination therapy, begun in September 1987, has had 11 patients entered so far.